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Sunday, March 13, 2011

Japan - Danger to the Public

According to Japanese authorities the radiation level near the explodedreactor 1 could be described by an equivalent dose of 50 µSv (micro-Sievert) which is generally regarded as rather harmless. In comparison with a value of 50 mSv per year which is the German standard limit for occupational exposure to ionizing radiation, that measured value can be interpreted as follows:50 mSv or 50.000 µSv per year is equal to 50.000 : 200 = 250 µSv perday (on 200 days of work!) or 250 : 24 = 10,4 µSv per hour.

Therefore, one might hold the measured 50 µSv to be an acceptable dose under the present circumstances of an exploded reactor.

Yet, it should be stressed that the equivalent dose H is by definition including a factor q intended to weigh the influence of the kind of radiation observed:X-rays, alpha-, beta- or gamma radiation with different wavelength or energy ( short wavelength means high energy ).

Now, the relative biological effectiveness (RBE) of radiation is known to differ in a range of about one order of magnitude depending of her energy. That leads to the necessity of determination what kind of radiation is present and refixing of the weighting factor q. A study made at the German university of Marburg has come to the conclusion that the standard weighting factor of one has to be reduced at least by a factor of 50-60. Same goes for the standard equivalent dose which must be reduced equally from 50 mSv per year to 1 mSv for occupational exposure. For public exposure a reduction from 1 mSv per year to 0,02 mSv per year has to be considered.

The proposed limit of 0,02 mSv per year for public exposure is equivalent to 20 µSv per year. Now compare these " 20 µSv per year " to the 50 µSv measured at the Japanese power plant at "time zero" after the explosion !

As we can assume that a broad variety of isotopes is leaving a broken reactor, and that such isotopes are falling apart by emitting different kinds of radiation, the real long-term danger to the public cannot be predicted. The measured isotopes of 137-Caesium for example are decaying by emission of some kind of beta-radiation that is usually regarded as especially harmful to human tissue.

By the way, many years ago I had been in charge of radiation security for my working group which includes a special preparation course to be finished with an examination. Such are the requirements in my country. Therefore, you can believe that I still know what I am talking about.

Next are the evening news of NHK World, Tokyo, recorded on March 13, 2011, 18:00 GMT:

Portrait of Ulysses

A resident of the global village and, as well, a lonely navigator on the internet, providing the information he finds on exotic websites in China, the Middle East and elsewhere in the world.
这就是《蓝图》杂志的新闻网站。
《游历子》是在古书画像的一个
希腊人，也是《蓝图》总编辑的
别名。两个人游览了世界的很多
地方，但是新式的《游历子》游
览世界网络的很多网站。